Curing coatings of a moisture-curable composition

ABSTRACT

An apparatus is provided with a chamber (20) into which a plurality of jets of moisture-laden air is directed through apertures (nozzles) 18. Through the chamber lasted shoes S, on the bottoms of which a coating of a moisture-curable adhesive composition has been applied, are progressively moved, supported bottom uppermost. The velocity of the air, which is re-circulated, is between 10 and 20 meters/second (measured at the apertures), its temperature is between 85° C. and 125° C. (measured at the point of impingement on the article) and its dew point not greater than 60° C. The lasted shoes are subjected to this treatment for a period of 1 to 31/2 minutes.

This invention is concerned with a process whereby a coating ofmoisture-curable composition applied to the surface of an article iscured and to apparatus for curing such a coating when applied to thebottoms of shoes.

There is described in our co-pending EP-A0079753 (EPC Application No.82305978.7) a method of treating an article, e.g. a shoe part, having acoating of a moisture-curable composition, in carrying out which methodthe article is placed in an enclosed chamber wherein it is subjected toinfra-red radiation and to which chamber a quantity of steam issupplied, the article remaining in the enclosed chamber for a period ofbetween 5 and 25 seconds for the purpose of curing the coating ofmoisture-curable composition. In addition, in said specification isdescribed an apparatus for use in carrying out the method.

Whereas the method and apparatus described in the aforementionedspecification ensures that the coating of composition is speedily andefficiently cured, nevertheless the apparatus does not in itself enhancethe possibility of a flow of production, since the loading and unloadingof shoes in the chamber, and also the opening and closing of thechamber, is essentially spasmodic.

It is therefore the object of the present invention to provide animproved apparatus for curing a coating of a moisture-curablecomposition, which apparatus is more suited for incorporation into acontinuously operating production line, and also to provide an improvedprocess whereby a coating of a moisture-curable adhesive can be cured,which process is readily adapted for use in a continuous productionflow.

There are hereinafter described in detail, to illustrate the inventionby way of example, an apparatus for curing a coating of moisture-curablecomposition applied to the bottoms of shoes, and a process whereby acoating of moisture-curable composition applied to the surface of anarticle is cured. The illustrative apparatus conveniently comprises achamber, conveyor means by which shoes can be conveyed, bottomuppermost, through the chamber, and means for supplying air to a plenumhaving an array of apertures extending over substantially the whole ofthe length of the chamber, said apertures opening into the top of thechamber whereby air supplied therethrough directly impinges on thebottoms of shoes being conveyed by the conveyor means. It will beappreciated that, from a work handling point of view, the mostconvenient way of conveying the shoes as aforesaid is bottom uppermost,since thereby they can rest with non-coated portions thereof in contactwith the supports. However, within the scope of the invention shouldalso be understood conveyor means of more complicated nature by whichthe shoes can be supported bottom down, in which case the plenum wouldbe situated beneath the conveying means and the apertures would openinto the bottom of the chamber.

The air supplying means of the illustrative apparatus supplies air asaforesaid at a velocity of the order of not less than 10 meters/second(measured at the apertures). The effectiveness of air velocity inachieving the desired results has been found not to be significantlyenhanced where the air velocity exceeds 20 meters/second and indeed,from the point of view of efficiency an air velocity not exceeding 15meters/second is preferred. Furthermore, an air velocity of not lessthan 13 meters/second is preferred for achieving the desired result in atime which is considered appropriate, as will be hereinafter referredto.

The distance of the apertures from the conveyor means is such that theair impinging on the bottom of a shoe supported by the conveyor means iseffective to "scrub" away the layer of air which usually is found to liestatic on the surface of the shoe bottom. To achieve this scrubbingaction, with air having a velocity as aforementioned it has been founddesirable that the shoe bottoms are spaced at a distance of the order ofnot more than 120 mm from the apertures; it is also desirable to arrangefor said distance to be not less than 75 mm, in order to be able toaccommodate shoes of different styles and sizes.

The speed at which the conveyor means of the illustrative apparatusoperates is variable, thereby varying the time taken for conveying ashoe through the chamber, operator-actuatable means being provided tothis end. In general, it has been found to be desirable to provide afacility for varying the time taken for the shoes to be conveyed throughthe chamber between 1 and 31/2 minutes; In using the illustrativeapparatus a preferred time has been found to be in the order of 11/2minutes ±1/2 minute. In this way, the amount of heat and moisture bywhich the coating of moisture-curable composition applied to the shoebottoms is treated can effectively be varied.

The illustrative apparatus further comprises means for heating the airsupplied by the air supplying means to a desired temperature. In generala temperature of not more than 125° C. has been found to be acceptable:furthermore with the type of composition for which the illustrativeapparatus is specifically intended the temperature should be not lessthan 85° C., preferably not less than 90° C. Furthermore for most suchcompositions a temperature not exceeding 100° C. has been foundadequate. The aforementioned temperatures are each as measured at thepoint at which the air impinges on the shoe bottoms. In some instancesit may be desirable to vary the temperature to which the air is heatedby the air heating means and to this end temperature varying means isprovided in the illustrative apparatus.

The illustrative apparatus further comprises means for supplying acontrolled amount of steam whereby the air in the chamber is maintainedat a dew point of not more than 60° C., preferably in the range 55° to60° C.; an optimum dew point is considered to be in the region of 56° C.The steam supplying means of the illustrative apparatus comprises aboiler having an electric heater element and means for controlling thelevel of water in the boiler in relation to the element, thereby in turnserving to control the amount of steam supplied.

The air supplying means of the illustrative apparatus by which air issupplied to the plenum comprises a fan by which air is drawn over heatermeans, e.g. electric heater elements, from a collecting chamber intowhich steam is supplied by the steam supplying means. In addition, airis ducted into the collecting chamber from the first-mentioned chamber,below the level of the conveying means, so that the air within theillustrative apparatus is continuously re-circulated with the constantaddition of steam from the steam supplying means. In this way, theenergy costs in maintaining the air at the required temperature aresignificantly reduced, as is also the need for ducting away the exhaustair after the treatment of the shoe bottoms.

In the illustrative apparatus the chamber through which shoes areconveyed by the conveyor means defines a generally U-shaped path forsuch shoes and to this end the conveyor means comprises an endless trackand a plurality of carriages, movable along said track, for supportingshoes bottom uppermost. For moving the carriages driving means isprovided which is arranged at a driving locality and by which thecarriages are successively engaged as they pass the driving locality,the arrangement being such that the carriage thus engaged is pushedagainst the carriages preceding it along said track, so that all thecarriages are thus advanced along said track. In the illustrativeapparatus the drive means comprises a multi-armed rotary drive memberwhich is caused to rotate continuously in the operation of theapparatus, and the arms of which are caused successively to pass throughthe driving locality and each to engage a carriage thereat.

It will thus be appreciated that by using conveyor means of this typeshoes can be conveyed from a loading position through the entry of thechamber, through the latter and out through its exit back to the loadingposition, so that both loading and unloading of shoes can be effected ata single position, whether by the operator or indeed automatically. Inaddition, it is convenient to arrange the driving locality for thecarriages adjacent to the entry of the exit end of the chamber. In thisway the drive means does not interfere in any way with and is notaffected by the atmosphere within the chamber.

In the illustrative apparatus each of the carriages of the conveyormeans has a pair of projecting support arms, or, more desirably, twopairs of such arms, the or each pair of arms being arranged such thatthe crown of a shoe last can be recieved therebetween for supporting theshoe bottom uppermost. Furthermore, the arms are mounted on the carriagefor heightwise adjustment thereon; it is expected that such adjustmentwould be necessary only in the case of a significant change of shoestyle or indeed when changing between e.g. men's shoes and ladies'shoes.

The illustrative apparatus is especially useful for carrying out theillustrative process, which is a process whereby a coating ofmoisture-curable composition applied to the surface of an article iscured. Such articles of course include lasted shoes but the processshould not be considered as being limited to the treatment of shoes. Theillustrative process comprises supporting the article with the coatingexposed and treating the coating with moisture-laden air directedthereat at a predetermined velocity, for a predetermined period andunder strict conditions of temperature and moisture control.

With regard to the control of the air being used, the velocity of theair, in carrying out the illustrative process, is in the order of notless than 10 meters/second, preferably not less than 13 meters/secondand, from the point of view of effectiveness and efficiency will notexceed 20 meters/second, preferably 15 meters/second, as discussedabove, with the nozzles through which the air is directed spaced at adistance in the order of not more than 120 mm from the surface to whichthe coating has been applied so that the air is directed in the form ofjets which impinge on the surface of the article, causing localturbulence with the effect that any surface layer of air surrounding thearticle is broken up, enabling the moisture-laden air being directed onto the article to contact it.

The air is directed thus against the article, in carrying out theillustrative process, for a period not exceeding 31/2 minutes,preferably for a period in the order of 11/2 minutes ±1/2 minute. Thishas been found to be generally sufficient, in combination with otherparameters, for ensuring that the moisture-curable composition willcure. It would of course be possible, during this treatment period, tomaintain the article in a static condition in relation to the nozzles,but in carrying out the illustrative process the article is movedrelative to the nozzles in a direction generally transverse of the jetsof moisture-laden air, and indeed the movement of the articles, incarrying the illustrative process, is in a direction extending generallywidthwise thereof. In this way it is ensured that the whole of thesurface of the article can be treated.

The temperature of the air, in carrying out the illustrative process, isin the order of not more than 125° C., more particularly 100° C., and ingeneral the temperature should be not less than 85° C., moreparticularly 90° C. In addition, the dew point of the air is not morethan 60° C., preferably 55° to 60° C.; an optimum dew point has beenfound to be in the region of 56° C.

It will be appreciated that both in respect of the illustrativeapparatus and of the illustrative process, various combinations of theforegoing features may be taken. Thus, the invention provides, in one ofits several aspects, an apparatus for curing a coating of amoisture-curable composition applied to the bottom of shoes, saidapparatus comprising a chamber, conveyor means by which shoes can beconveyed, bottom uppermost, through the chamber, and means for supplyingair to a plenum having an array of apertures extending oversubstantially the whole of the length of the chamber, said aperturesopening into the top of the chamber whereby air supplied therethroughdirectly impinges on the bottoms of shoes being conveyed by the conveyormeans, wherein said air supplying means supplies air as aforesaid at avelocity of 10 to 20 meters/second (measured at the apertures), andwherein the apparatus further comprises means for heating the air to atemperature of between 85° C. and 125° C. (measured at the point atwhich it impinges on the shoe bottoms) and means for supplying acontrolled amount of steam whereby the air in the chamber is maintainedat a dew point of not greater than 60° C.

In addition, the invention also provides, in another of its variousaspects, a process whereby a coating of moisture-curable compositionapplied to the surface of an article is cured, said process comprisingsupporting the article with the coating exposed, and directing at saidcoating, for a period of between 11/2 and 31/2 minutes, a plurality ofjets of moisture-laden air from nozzles spaced at between 75 and 120 mmsfrom the surface to which the coating has been applied, wherein thevelocity of the air is between 10 and 20 meters/second, its temperatureis between 85° C. and 125° C., and its dew point is not greater than 60°C.

There now follows a detailed description, to be read with reference tothe accompanying drawings, of the illustrative apparatus and theillustrative process, from which description the various objects andaspects of the present invention will be made apparent. It will ofcourse be appreciated that the illustrative apparatus and theillustrative process have been selected for description merely by way ofnon-limiting example.

In the accompanying drawings:

FIGS. 1 and 2 are respectively plan and side views of the illustrativeapparatus; and

FIG. 3 is a fragmentary view of a carriage forming part of conveyormeans of the illustrative apparatus.

With reference to FIGS. 1 and 2, the illustrative apparatus comprises abase 10 having upstanding support members 12 on which upper and lowertrack members 14,16 are mounted, one above the other, defining anendless oval-shaped track, as will be referred to hereinafter.Surrounding the track is a chamber 20 which is closed at the top by aperforated lid 22 which also forms the floor of a plenum chamber 24arranged above the track 14,16 and chamber 20. The lid 22 is perforatedin a regular manner to provide an array (in the form of a plurality ofrows) of apertures 18, each row extending radially of the oval track.Beneath the track 14,16, centrally disposed within the oval shapethereof, is a ducting 26 which opens into the plenum chamber 24 at itstop and at its bottom is connected to a housing 28 for a fan generallydesignated 30. The fan is driven by the suitable electric motor 31sufficient to provide an air velocity of at least 12 meters/secondmeasured at the apertures 18 in the perforated lid 22. The fan draws airfrom a collecting chamber 32 and during such drawing the air passes overa series of electric heater coils 34 arranged adjacent to the fan inlet.The floor of the chamber 20 has an elongated opening 34, extendingbeneath one side portion of the oval track 14,16 and this opening 34opens into the top of the collecting chamber 32. A plurality of holes 36is also provided in the floor of the chamber 20, beneath the other sideof the track 14,16, which holes 36 are connected by ducting 38 to thecollecting chamber 32. In this way air can be uniformly exhausted fromthe chamber 20 to the collecting chamber 32. In addition, a boiler 40 isprovided which is connected by ducting 42 to the collecting chamber 32for supplying steam, and thus moisture, to the air in the collectingchamber 32. It will thus be observed that under the action of the fan 30air is continuously re-circulated through the chamber 20 and during suchre-circulation is heated by the heater elements 34 and laden withmoisture by the boiler 40.

For conserving heat, the walls of the plenum chamber 24 and the chamber20, collecting chamber 32 and fan housing 28 are all lagged. Inaddition, an outer cover 44 is provided, which enhances appearance aswell as assisting insulation. Furthermore, in order to ensure that thereis no excessive heat loss at the side of the chamber 20 opposite theopening 34, a yieldable wall member (not shown) in the form of aplurality of sets of bristles is provided, extending from the floor ofthe chamber up to just beneath the conveyor means. Using bristles, thismember does not impede the passages of e.g. high-legged boots passingthrough the chamber 20.

The temperature of the air in the chamber 20 is regulated in any desiredmanner, as will be hereinafter referred to, and in addition the rate ofsupply of steam from the boiler 40 is controlled. In the latter case, toensure a constant supply of steam, the control takes the form ofcontrolling the level of the water in the boiler in relation to anelectric heater element 46, thereby regulating the amount of steamproduced. In order thus to control the level of the water a topping uptank 48 is provided. For temperature control, furthermore, means isprovided in a form of variable thermostat (not shown) by which theoperator can vary the temperature to which the air is heated by theheater elements 34, according to the required parameters, as will bereferred to hereinafter.

The chamber 20 of the illustrative apparatus is generally U-shaped,having entry and exit openings indicated by arrows A,B from whichproject one end of the track 14,16. In the illustrative apparatus theopening 34 is arranged at said one side of the chamber 20 leading to theexit opening and the holes 36 are arranged at said other side adjacentthe entry opening.

The track 14,16 forms part of conveying means of the illustrativeapparatus and serves to support a plurality of carriages generallydesignated 50, each of which is supported by upper and lower wheels 52,54 running respectively on the upper and lower tracks 14,16. Eachcarriage 50 comprises an angled plate 56 on which the rolls 52, 54 aresupported, the plate having secured thereto an angle member 58 on whichtwo pairs of support arms 60 are secured, the arms 60 (as can be seen inFIG. 3) projecting outwardly from the angle member 58 and thus radiallyand outwardly from the track 14,16 into the chamber 20. The angle member58 is mounted for heightwise adjusting movement on the plate 56 bypin-and-slot connections (see FIG. 3). Each pair of support arms 60 isarranged to receive between the arms the crown (or cone) of the last ofa lasted shoe such that the shoe is supported by the arms bottomuppermost, i.e. with the shoe bottom facing the apertures 18 openinginto the chamber 20. The arms are spaced from the apertures 18 by adistance of between 75 and 120 mm; ideally the bottoms of shoessupported by the arms 60 should be spaced from the apertures by adistance of some 55 mm.

For moving the carriages 50 along the track 14,16, drive means generallydesignated 62 is provided comprising a drive shaft 64 on which aplurality of (in casu seven) arms 66 which are movable in a horizontalplane. As the shaft 64 rotates, therefore, carrying the arm 66therewith, rolls 68 on the carriages 50 in the vicinity of theentry/exit end of the conveyor means can be engaged by one of said arms,thereby serving to advance that carriage 50 along the track 14,16. Eachcarriage 50, furthermore, is arranged to move the carriage preceding italong the track 14,16 by pushing thereagainst so that by the action ofthe drive means 62, the carriages are advanced along the track. Forcausing the rotation of the shaft 64, the drive means 62 furthercomprises a chain-and-sprocket drive generally designated 69 whichconnects the shaft 64 with an output drive shaft 70 of a gear box 72driven by an electric motor 74, the gearbox and motor being mounted on asupport plate 76 carried by the forward support members 12 of theillustrative apparatus. The motor 74 operates continuously in theoperation of the illustrative apparatus, so that the carriages 50 aremoved continuously, or substantially continuously along the track 14,16.

Whereas the illustrative apparatus described above is provided withsupport arms 60 by which shoes can be supported bottom uppermost, inother apparatus in accordance with the invention otherwise generallysimilar to the illustrative apparatus the conveyor means may be adaptedto support shoe soles on a surface of which a coating of amoisture-curable composition has been applied, and the scope of thepresent invention should also be read as embracing the treatment of shoesoles mutatis mutandis; thus where appropriate, reference to supportingthe articles "bottom uppermost" should be understood as indicating"coated surface uppermost".

In using the illustrative apparatus in carrying out the illustrativeprocess, shoes S are mounted, if desired in pairs, on the carriages at aloading station adjacent to the entry end A of the chamber 20, as thecarriages are progressively moved through the chamber. The shoes are ofcourse supported bottom uppermost on the support arms 60, that is withthe shoe bottoms facing the apertures 18 in the lid 22 of the chamber20. The parameters required for the illustrative process are that theair should be impelled towards the surface of the shoe bottom at avelocity of between 10 and 20 meters/second (as measured at theapertures 18) and impinge thereon and the temperature of the air shouldbe between 85° C. and 125° C., preferably between 90° C. and 100° C.with an optimum temperature in most cases of 95° C. Furthermore, the airshould be moisture-laden such that its dew point is not greater than 60°C., preferably between 55° and 60° C.

The shoes are of course continuously moved along the chamber 20 so thatthey are moved relative to the apertures (or nozzles) 18 and thussuccessively passed the jets of moisture-laden air. The manner in whichthe shoes are supported by the carriages 50, ensures that the shoes aremoved in a direction extending widthwise of their bottoms pastsuccessive rows of apertures 18 extending radially about the oval-shapedtrack 14,16. In this way the shoe bottom is successively "swept" by thejets of moisture-laden air.

The speed of the conveyor means (and ultimately the output speed of themotor 74) is so set that the shoes are moved through the whole of thechamber 20 in a period of between 1 and 31/2 minutes; an optimum periodis considered ±1/2 minute.

It has been found that with these ranges of parameters, moisture-curablecomposition coatings on shoe bottoms can be readily cured within thetime set, without subjecting the shoes themselves to damage caused byexcessive heating or indeed water damage. Furthermore, because of thecontinuous operation of the conveyor means, and the continuous trackpassing through the U-shaped chamber 20, the work handling of the shoesto be treated is rendered convenient for one operator to perform, withconsequent improvement in productivity and efficiency.

EXAMPLE

In carrying out one example of a process in accordance with theinvention a layer, 0.01 mm thick, of Bostik Supergrip 9801 adhesivecomposition was applied to the bottom of each of a plurality of lastedshoes for the subsequent attachment thereto of sole units. ("Bostik" isa Registered Trade Mark in respect of, inter alia, adhesivecompositions.) This composition, which is available from Bostik Ltd.Ulverscroft Road, Leicester, is a moisture-curable composition of thepolyurethane prepolymer type, and has a viscosity of 22 Newtons/meters²at its application temperature of 100° C.; this enables it to be appliedin relatively thin layers, especially when a nozzle of the typedescribed and claimed in GB-A 2098884 is used.

In addition to each shoe bottom, each sole unit also had a coating ofthe same composition applied thereto in a similar thickness. In the caseof the sole units, curing of the adhesive composition may, if desired,take place in atmosphere; the cure time is then between 8 and 72 hours,depending upon film thickness, porosity of the substrate and therelative humidity of the atmosphere. This enables the sole units to becoated before being brought to the production line.

The coated shoe bottoms were, following application, immediately placedon the support arms 60 of illustrative apparatus at the load/unloadstation, and were carried through the chamber 20, as above described.The apparatus was set up with the following parameters:

Air velocity--14 meters/second (measured at the nozzles)

Air temperature--95° C.

Air dewpoint--56° C.

Conveyor speed--timed to carry shoes through the chamber in 11/2minutes.

It was found that, using the illustrative apparatus set up as aforesaid,the adhesive coating was substantially completely cured within the timestated.

The coated shoes were then transferred to the next operation, which wassole attaching. In this operation activation of the coating on the soleunit and, if necessary, the coating on the shoe bottom also, took placeusing an activator of the type described in EP-A 0092320, whereafter thesole unit was bonded to the shoe bottom using a conventional soleattaching press.

We claim:
 1. A process whereby a coating of moisture-curable compositionof the polyurethane prepolymer type applied to the surface of an articleis cured, said process being characterised by providing a plurality ofnozzles, supporting the article with the coating exposed, and directingat said coating, for a period of between 1 and 31/2 minutes, a pluralityof jets of moisture-laden air from said nozzles spaced at between 75 and120 mms from the surface to which the coating has been applied, whereinthe velocity of the air is between 10 and 20 meters/second, itstemperature is between 85° C. and 125° C., and its dew point is notgreater than 60° C.
 2. A process according to claim 1 characterised inthat the dew point is between 55° C. and 60° C.
 3. A process accordingto claim 2 characterised in that the dew point of the air is in theregion of 56° C.
 4. A process according to claim 1 characterised in thatthe temperature of the air is between 90° C. and 100° C.
 5. A processaccording to claim 1 characterised in that the temperature of the air is95° C.
 6. A process according to claim 1 characterised in that the jetsof moisture-laden air are directed at the coating for a period of 11/2minutes ±1/2 minute.
 7. A process according to claim 1 characterised inthat the article is constituted by a lasted shoe having a coating ofmoisture-curable composition applied to the bottom thereof.
 8. A processaccording to claim 7 characterised in that the shoe is moved relative tothe nozzles in a direction extending generally widthwise of the shoebottom.